EP0875899B1 - Arrangement of two memories on the same monolithic integrated circuit - Google Patents

Description

The invention relates to an integrated circuit. monolithic with two memories, preferably separate from each other, and circuits electronic to allow operation in simultaneous of the two memories.

It particularly applies to briefs non-volatile, programmable and erasable electrically EEPROM, flash EPROM or memories saved by battery. Each of the memory cells of these first two memories consists of a floating gate transistor having a gate command, a floating grid, a source region and a drain region. To write or read such a cell memory, we apply specific voltages on connections that lead to these cells. These tensions depend on memory types.

For example to program a memory cell in an EEPROM memory, we apply to the line of words, connected to the control gate of the transistor floating grid of the memory cell, a voltage strongly positive and to the bit line connected to the region drain a zero voltage. The application of these tensions creates through the narrow oxide layer a high tension resulting in migration of electrons to the floating gate. These electrons are trapped in the floating grid. The phenomenon put at stake is a tunnel phenomenon.

In another example, to program a memory flash EEPROM type, the voltages applied to various electrodes of a memory cell are different. During programming, a strong positive voltage at the word line of the transistor a memory cell. We apply a voltage intermediate, for example positive of the order of 5V, to the drain region. Just like in a type memory EEPROM, the application of these voltages cause a electron migration. The phenomenon involved is a phenomenon known as hot carriers.

There is therefore a certain disparity between the programming and reading voltages, both for the same memory and both for memories of different types.

On a monolithic integrated circuit, integrating including memories of different types, we want however keep the possibility of operation simultaneous as if the two memories were not not on the same integrated circuit. We also want use memories of different types on the same integrated circuit because the different types lead to different characteristics: speed more or less large writing capacity, integration density, accessibility bit by bit or page by page. A designer can then, with the same integrated circuit, to have faculties that allow him to organize himself better.

It is known in the state of the art to have the same integrated circuit comprising two memories distinct from each other. However the possibility of performing simultaneous operations on these two memories is limited. We know how to read or write to a flash EPROM memory, while reading or writing to an EEPROM type memory, provided you duplicate all the useful functions. This means doubling of buses and circuits to which they are connected. State of the art offers no alternative. The problem presented is that these functions then occupy a lot of space on the integrated circuit and reduce its efficiency. In particular the fact of having two buses is unacceptable. Yes there is only one bus, the functioning of the memories is not not simultaneous, it is alternative. In this case there is a waste of time.

The object of the invention is to remedy this problem by allowing writing or reading in a memory while writing or reading is allowed in the other memory, these two memories being present on the same integrated circuit. Preferably, there is than a bus.

In practice, the invention proposes to remedy this problem in allowing to select one or the other memories and write operations there or reading while the other memory is in read or write. In the invention we take advantage that a programming or reading operation lasts a certain predetermined time, which is specific to each memory. Rather than being embarrassed, we use the memory occupation time at one of these tasks to isolate it, select the other memory, and start executing this other memory read or write. So we use a selection signal to start a task. The continuation of the task is conditioned by a signal hold triggered by this selection signal.

Thus, the subject of the invention is an integrated circuit monolithic with two separate memories one on the other, a microcontroller to sequence write or read operations of these memories, a selection circuit suitable for selecting one or the other from the memories and receiving a signal from selection. The invention is characterized in that the integrated circuit has two microcontrollers in relationship each with one of the memories and in that each microcontroller has a circuit for execute in each memory the write operations or reading regardless of the signal value of selection.

In one example, to solve the problem of specific voltages to apply for a type particular from memory, we duplicated pumps charge. Thus, the set constituted by the microcontroller and charge pumps allows perform programming or reading in each memory independently one of the other.

• figure 1 : la représentation schématique d'un circuit conforme à l'invention;
• figure 2 : des diagrammes temporels de signaux utilisés dans l'invention.

The invention will be better understood on reading the description which follows and on examining the figures which accompany it. These are given for information only and in no way limit the invention. The figures show:

• Figure 1: the schematic representation of a circuit according to the invention;
• Figure 2: time diagrams of signals used in the invention.

In Figure 1, an integrated circuit is shown 1 comprising two memories, 2 and 3, distinct from one the other. In one example, in addition to being separate, the two memories are of different types: memory 2 is an EEPROM, memory 3 is a flash EPROM. A microcontroller 4 is capable of causing execution in sequence of write and / or read operations in these memories 2 and 3. A microcontroller is a microprocessor with dedicated program memory. A microcontroller only knows in practice what to do actions recorded in program memory. A selection circuit 5 selects one or the other of these memories 2 or 3. In an example, a double selection signal SS1 and SS2 is applied to the input of this circuit 5. The signals SS1 and SS2 are complementary. According to the invention, the integrated circuit 1 comprises a second microcontroller 6 of the same type. The two microcontrollers 4 and 6 are in relation each with one of memories 2 and 3 respectively.

An address decoder 7 is controlled by the microcontroller 4. The decoder 7 allows access to the memory 2. Similarly, an address decoder 8 is controlled by the microcontroller 6. The decoder 8 allows access to memory 3.

According to the invention, each microcontroller 4 and 6 has a circuit, respectively 13 or 14 or 25 or 26, to execute in each memory the operations writing or reading, regardless of value selection signal SS1 or SS2. For this purpose, a validation input 9 and 10 of each microcontroller respectively is connected, in an example, to the output of an OR gate 11 and 12 respectively with two inputs. With these two entries we want to validate these write or read microcontrollers.

A first of the inputs of each gate OR 11 and 12 is connected to the selection circuit 5 by through circuits 13 and 14 suitable for supplying a write delay signal of duration T or T '. Circuits 13 and 14 are triggered during a write selection and produce a sustained signal SME1 (write hold signal) during this duration T or SME2 for a duration T '.

The circuits 13 and 14 can for example be monostable multivibrator circuits. Alternatively, the circuits 13 and 14 are an integral part, with the OR gates 11 and 12, microcontrollers 4 and 6. In in this case, circuits 13 and 14 can be made up of metering firmware by microcontrollers 4 and 6. These microprograms of counting count for example a predetermined number of pulses of a clock signal produced by or supplied to the microcontroller.

The duration T of the signal SME1 is chosen in such a way so that it is greater than or equal to a duration execution of a write in memory 2. There may also have two durations: a long duration T for a writing, a duration T "for a reading. We will see below how the distinction operates.

The inputs of circuits 13 and 14 are connected to door outputs AND respectively 15 and 16 to two entries. Doors 15 and 16 form a first circuit logic 21. A first entry of gate 15 is connected to a first entrance to door 16 by a connection 17. Connection 17 receives a command of writing E common to the two memories 2 and 3. The circuit 21 also receives on the second inputs of doors 15 and 16 selection signals SS1 and SS2 respectively. These signals allow select one of memories 2 or 3 for writing in function of the logic level of the two signals SS1 or SS2 selection and level of signal E.

The second entrances to these doors 15 and 16 are connected to connections that carry signals from SS1 and SS2 selection respectively via of a circuit 18 with two inputs and two outputs. The circuit 18 consists of two looped reversers 19 and 20 in parallel on its two entrances and its two exits. Circuit 18 ensures the selection of a single of the two memories at the same time. Connection 22 which connects the output of the inverter 19 and the input of the inverter 20 constitutes both an entry and an exit from this circuit 18 connected to door 15. Connection 23 which connects the output of the inverter 20 and the input of the inverter 19 constitutes both a second input and a second output of this circuit 18 connected to the door 16. The two inputs of circuit 18 correspond selection signals SS1 and SS2. We don't select only one memory at a time insofar as one does not want not duplicate memorizations. However, in a mirror use, circuit 18 can be omitted, both memories can be selected at the same time time.

OR doors 11 and 12 have a second Entrance. The second entrances of these doors 11 and 12 are also connected to a timer circuit, by example here also a monostable multivibrator, 25 and 26 respectively. These two circuits 25 and 26 have the same functions as the two circuits 13 and 14 previously defined and are similarly related to the selection circuit 5. OR doors 11 and 12 receive maintained signals (SME1 SME2 and SML1 SML2 depending on the writing or reading mode selected) of reading and writing. They deliver a hold signal, during the write or read operation selected, in the selected microcontroller.

The selection circuit 5 thus comprises a second logic circuit 24. This circuit 24 is of identical to circuit 21. It has two AND gates 27 and 28 whose outputs are connected to inputs of circuits 25 and 26 respectively. circuit 24 has three inputs. A first entry of door 27 is connected to a first entrance to the door 28 by a connection 30 and constitutes a first input of circuit 24. Connection 30 receives a read command L common to the two memories 2 and 3. Circuit 24 also receives on the second inputs of doors 27 and 28 selection signals SS1 and SS2 to allow you to select one of these memories 2 or 3. These signals allow selection from memory exclusively.

Each of memories 2 and 3 has circuits address and data decoders 7 and 29 and 8 and 31. In accordance with the invention, the address decoders are duplicated to allow a address decoding for each of memories 2 and 3, independently of each other. The decoder 7 address is connected to microcontroller 4 and to the lines of words from memory 2. Decoder 8 is connected to microcontroller 6 and word lines from memory 3. These decoders 7 and 8 receive the addresses to decode by address buses 32 and 33 respectively whose number of lines is characteristic of memories 2 and 3. Buses 32 and 33 are both from of the same address demultiplexing circuit 34. The circuit 34 receives at its input a bus 37 with address, common to both memories 2 and 3. Bus 37 is connected to the pins (not shown) of the integrated circuit 1. Buffers respectively 35 and 36, controlled by microcontrollers 4 and 6 allow to memorize the bits of the addresses transmitted by the demultiplexer 34.

The two memories 2 and 3 are connected to another data decoder 29 and 31 respectively. decoders 29 and 31 receive data signals to apply to the bit lines of memories 2 and 3. Charge pumps 320 and 330 are connected, respectively, at the outputs of decoder 29 and at memory 2, and at the outputs of decoder 31 and at memory 3. The charge pumps are controlled by the corresponding microcontroller. These pumps allow to polarize the lines of each of memories independently of each other. Indeed, the presence of these pumps makes it possible to polarize the lines of each of memories 2 and 3 to potentials different and therefore read or write simultaneously in each of the memories.

Each decoder 29 and 31 is connected to a bus 39 and 40 of data respectively from a circuit of demultiplexing 38 of data. In order to memorize the data to be programmed, buffers 41 and 42 are installed on these buses respectively 39 and 40 in output of the demultiplexer 38. These buffer memories 41 and 42 are controlled by microcontrollers 4 and 6 respectively. The demultiplexer 38 is connected to its input to a data bus 43 common to both memories. Bus 43 is connected outside the circuit 1.

Each memory 2 or 3 can have a bus 46 and 47 data output respectively. These buses 46 and 47 are connected to memories 2 and 3 by read circuits 48 and 49 respectively by microcontrollers 4 and 6. As a variant, the circuits 48, 29 and 320 are connected to the same bus input output 39-46. Likewise, alternatively, the circuits 49, 31 and 330 are linked to the same input bus data output 40-47. In this case circuits 48 and 29, and 49 and 31 are produced in the form of a single circuit every time. In this case too, the demultiplexer 38 can be used as a multiplexer for output data on bus 43.

We will now explain how a like multiplexer. Circuits 48 and 49 deliver in data output whose number of bits depends on number of bus lines 39 or 40. In an example, there are eight bit lines each time and we form eight bit words. Each of the bits read in a word in a memory is applied to the entry of an element multiplexer 50 with two inputs. The other entry of this multiplexer element 50 is dedicated to a bit read in a word in the other memory. There is preferably correspondence between the length of words read or written in one memory and those read or written in another. This is however not an obligation. There is as much of multiplexer elements 50 that the longest word to read from memory has bits.

The multiplexer element 50 has two inputs identical scales 51 and 52. The inputs of the scales 51 and 52 are connected to one of the wires of buses 46 and 47 respectively. Each rocker 51 and 52 is made up of two identical doors. For example, flip-flop 51 has an AND 53 door with three inputs and a door OR 54 with three entries. A first door entrance AND 53 is connected by a connection 55 and by a inverter 56 at an entrance to the OR gate 54. The connection 55 is also connected to the output of the circuit 25. A second entrance to gate 53 is connected to the exit of door 54. Conversely the output of door 53 is connected to a second input of door 54. The third entrances of doors 53 and 54 are connected together to a wire 70 of the bus 46. The second rocker 52 included in the element multiplexer 50 is identical to flip-flop 51 set to except that the signals that control it come from the other timer circuit 26 via a connection 73. On the other hand, a connection 69 equivalent to the connection 70 of the first rocker is connected to the reading circuit output 49.

The two flip-flops 51 and 52 each have two exits. The outputs of the OR doors (54) of both flip-flops 51 and 52 are connected to the two inputs an AND 57 door with two inputs. The outputs of AND gates (53) of the two flip-flops 51 and 52 are connected to the two inputs of a door OR two 58 entries. These two doors 57 and 58 have their outputs applied to order grids respectively a P 59 type MOS transistor and a MOS transistor N 60 type. These two transistors are in series. The source of transistor 59 is connected to potential Vcc, integrated circuit power supply. The transistor drain 60 is connected to ground. The output of the element multiplexer 50 is located at the midpoint of the two transistors 59 and 60 arranged in series.

The midpoint of transistors 59 and 60 is connected to a connection 71. There are as many connections 71 that there are multiplexer elements 50. The connections 71 together form the data output bus 72 of the integrated circuit 1.

The multiplexer element 50 is connected by the connection 55 at the output of circuit 25. In this way it is controlled by the read selection signal L after the transformation of this signal L into signal SML1, maintained by circuit 25. The signal SML1 allows output the data from the memory selected.

In another example, the multiplexer 50 can be directly controlled by the read signal. This solution is shown in dashes in Figure 1. In this in this case the selection signals must be imposed outside circuit 1 at a time when the selection in reading and when outputting data on bus 72.

The signal present on connection 55 allows according to the cases of inhibiting the flip-flop 51 or on the contrary of the make passers-by.

We will now describe with reference to FIG. 2 a mode of use of the circuit of figure 1. This mode highlights the functioning of the two microcontrollers 2 and 3 running in each memory write operations independently.

We consider here that the control signal E is active. The top of Figure 1 shows that signal E is active (at level 1) while the signal L is inactive. This complementarity, usual, however, is not necessary. In the case from memory 2 selection, apply to input of selection circuit 5, for example on date t, a selection signal SS1 active (level 1). Circuit 18 automatically sets the signal SS2 to select the memory 3 at a complementary logic level (inactive). The selection signal SS1 triggers a signal SME1 from time delay, duration T, via the circuit 13. This produces a sustained signal SME1 characteristic of a write selection of the memory 2. The duration T of this signal SME1 is greater or equal to the duration of execution of a write. The microcontroller 4 is therefore validated by this signal from duration T applied to door 11. It is at the same time isolated from the outside, insensitive to fallout 74 SS1 signal or even a possible untimely signal 75.

The holding signal produced at the output of the door 11 gives the order to the microcontroller to execute in memory 2 the write operation. The addresses AD1 sent on bus 37 following the order E, or SS1 selection, are present at the output of address demultiplexer 34. The demultiplexer 34 correctly directs addresses that he receives, either because he receives an order in this sense of microcontroller 4, either because it discriminates according to the address read on the bus 37 that of buffers 35 or 36 which must be requested. In variant, the two buffer memories 35 and 36 have the same addresses, and the microcontroller 4 validates the address buffers 35 and data 41 that the microcontroller 6 validates the buffer memories 36 address, and 42 data, by connections 76 to 79 respectively. In this case microcontrollers 4 and 6 for this purpose interpret the signals delivered by the OR gates 11 and 12. AD1 address bits stored in the buffers 35 are applied to the decoder 7. They allow you to select one or more lines of memory word 2.

In the same way the data D1 is present at the output of the data demultiplexer 38 and at the input of the buffer memory 41. The charge pump 32 is activated at the same time as the buffers. She allows to polarize the bit lines of the memory to programming voltages. Under these conditions, on the base of AD1 addresses available in memory buffer 35 and D1 data available in memory buffer 41, microprocessor 4 (which continues to be validated by the order of duration T) causes the desired programming in memory 2.

Once SS1 selection has resulted in trigger these actions, signal SS1 may drop, after or before the transfer of data or addresses in buffers 41 and 35, depending on the mode normal or according to the variant mode selected. In the normal mode, address and data transfers may even be prior to order SS1 if the control of demultiplexers 34 and 38 is external.

At the time of the falling edge 74 of the signal selection SS1, signal SS2 becomes active. He authorizes a selection from memory 3. The selection signal SS2 triggers, if the write signal has remained active, a time delay signal SME2 T 'from the circuit 14. The duration produced by circuit 14 is not not necessarily the same as the duration T of the circuit 13. It depends on the programming speed of the memory 3 compared to that of memory 2. A signal holding is produced accordingly at the exit of the logic circuit 12 to validate the microcontroller 6. The microcontroller 6 then becomes autonomous in turn and can execute the write to memory operation 3.

The write operations are simultaneous in the two memories if the front 74 occurs before the end of the duration T. Figure 2 shows, downwards, the AD2 address and D2 data transfers useful for memory programming 3.

From the moment the delay signal is triggered, the microcontroller operates and performs write operations regardless of value of the selection signal. So we take advantage of this duration of autonomy to trigger writing in the other memory.

The invention particularly finds a application in functional tests for which the length of the test time is a factor of productivity. Write and read operations can be performed in two separate memories of the same integrated circuit, this reduces test time and a fortiori the cost of the test.

All that has just been said for writing is valid for reading. To the extent that a write operation lasts around 500 microseconds, we see the interest in run two at the same time. For reading, it suitable, on a reading cycle of a few microseconds, to remember that a cell reading proper lasts for about 100 nanoseconds. With the process of the invention, we start reading in a memory. While it continues, we start the read in the other. Then we can reselect (in synchronizing) bus 46 of the first memory (then bus 47) with the multiplexer elements 50 for ensure the transfer of the data read on the bus 71.

In the case of reading, of course, it is only necessary that the durations T "and T" 'of SML1 and SML2 signals delivered by circuits 25 and 26 (which can be equal to each other) is greater or equal to the playing times. They can be also greater than or equal to the write times well let it be of little use.

Claims (11)

1. Integrated circuit (1) comprising two memories (2, 3) separate from one another, a microcontroller (4) for sequencing writing or reading operations for these memories (2, 3), a selection circuit (5) suitable for selecting one or other of the memories (2, 3) and receiving a selection signal (SS1, SS2), characterised in that

   this integrated circuit (1) comprises two microcontrollers (4, 6) each in relation with one of the memories (2, 3), and in that

   each microcontroller (4, 6) comprises a circuit (13, 14) for executing the writing or reading operations in each memory (2, 3) independently of the value of the selection signal (SS1, SS2).
2. Circuit according to claim 1, characterised in that each microcontroller (4, 6) is connected to the selection circuit (5) through the intermediary of means (13, 14) suitable for supplying a delay signal of a given time (T), triggered when a selection is made, to produce a holding signal (SME1, SME2) during this given time, the given time being greater than or equal to a time for execution of a reading or a writing operation.
3. Circuit according to one of claims 1 to 2, characterised in that it comprises

   a circuit (18) so that the selection signals are complementary in order to select just one memory (2, 3) at a time.
4. Circuit according to one of claims 1 to 3, characterised in that

   the selection circuit (5) comprises at least a first logic circuit (21) which receives a writing command (E) common to the two memories and which receives the selection signal (SS1, SS2), the logic circuit (21) permitting the selection (SME1, SME2) of one of these two memories (2, 3) for writing.
5. Circuit according to one of claims 1 to 4, characterised in that

   the selection circuit (5) comprises a second logic circuit (24) which receives a reading command (L) common to the two memories (2, 3) and which receives the selection signal (SS1, SS2), the logic circuit (24) permitting the selection (SME1, SME2) of one of these two memories (2, 3) for reading.
6. Circuit according to one of claims 4 or 5, characterised in that the logic circuit (24) comprises two gates (27 and 28) with two inputs, a first input of these gates receiving the selection signal (SS2, SS1), a second input receiving the writing or reading signal, to permit selection of a memory exclusively for writing or for reading.
7. Circuit according to one of claims 1 to 6, characterised in that it comprises

   duplicated address decoders (7, 8, 29, 31) to permit decoding of addresses in each of the memories (2, 3) independently of one another.
8. Circuit according to one of claims 1 to 7, characterised in that it comprises

   duplicated charging pumps (32, 33) to polarise lines in each of the memories (2, 3) independently of one another.
9. Circuit according to one of claims 1 to 8, characterised in that it comprises

   an OR gate at the validation input of each microcontroller (11, 12) to receive the reading and writing holding signals and to produce a holding signal during the writing or reading operation.
10. Circuit according to claim 5, characterised in that it comprises

    an output multiplexer (50) controlled by reading signals (73) from the second logic circuit (24) and which supplies the data read from the selected memory (2, 3) at the output.
11. Circuit according to claim 5, characterised in that it comprises

    an output multiplexer (50) controlled (55) by the holding signals (SML1) suitable for supplying the data read from the selected memory at the output.

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